Chemically amplified resist composition and patterning process

ABSTRACT

A chemically amplified resist composition comprising a quencher containing a quaternary ammonium iodide, dibromoiodide, bromodiiodide or triiodide, and an acid generator exhibits a sensitizing effect and an acid diffusion suppressing effect and forms a pattern having improved resolution, LWR and CDU.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2016-224748 filed in Japan on Nov. 18,2016, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a chemically amplified resist compositioncomprising a quencher containing a quaternary ammonium salt, and an acidgenerator, and a patterning process using the same.

BACKGROUND ART

To meet the demand for higher integration density and operating speed ofLSIs, the effort to reduce the pattern rule is in rapid progress. Thewide-spreading flash memory market and the demand for increased storagecapacities drive forward the miniaturization technology. As the advancedminiaturization technology, manufacturing of microelectronic devices atthe 65-nm node by the ArF lithography has been implemented in a massscale. Manufacturing of 45-nm node devices by the next generation ArFimmersion lithography is approaching to the verge of high-volumeapplication. The candidates for the next generation 32-nm node includeultra-high NA lens immersion lithography using a liquid having a higherrefractive index than water in combination with a high refractive indexlens and a high refractive index resist film, EUV lithography of 13.5 nmwavelength, and double patterning version of the ArF lithography, onwhich active research efforts have been made.

The exposure system for mask manufacturing made a transition from thelaser beam exposure system to the EB exposure system to increase theaccuracy of line width. Since a further size reduction becomes possibleby increasing the accelerating voltage of the electron gun in the EBexposure system, the accelerating voltage increased from 10 kV to 30 kVand reached 50 kV in the current mainstream system, with a voltage of100 kV being under investigation.

As the pattern feature size is reduced, approaching to the diffractionlimit of light, light contrast lowers. In the case of positive resistfilm, a lowering of light contrast leads to reductions of resolution andfocus margin of hole and trench patterns.

As the pattern feature size is reduced, the edge roughness (LWR) of linepatterns and the critical dimension uniformity (CDU) of hole patternsare regarded significant. It is pointed out that these factors areaffected by the segregation or agglomeration of a base polymer and acidgenerator and the diffusion of generated acid. There is a tendency thatas the resist film becomes thinner, LWR becomes greater. A filmthickness reduction to comply with the progress of size reduction causesa degradation of LWR, which becomes a serious problem.

The EUV lithography resist must meet high sensitivity, high resolutionand low LWR at the same time. As the acid diffusion distance is reduced,LWR is reduced, but sensitivity becomes lower. For example, as the PEBtemperature is lowered, the outcome is a reduced LWR, but a lowersensitivity. As the amount of quencher added is increased, the outcomeis a reduced LWR, but a lower sensitivity. It is necessary to overcomethe tradeoff relation between sensitivity and LWR. It would be desirableto have a resist material having a high sensitivity and resolution aswell as improved LWR and CDU.

Patent Document 1 proposes a quencher of iodonium carboxylate typehaving a carboxylate ion bonded to an iodonium cation. Patent Documents2 and 3 propose the use of hypervalent iodine compounds as the quencher.Since iodine has a high atomic number, quenchers in the form ofiodinated compounds are fully effective for suppressing acid diffusion.

CITATION LIST

-   Patent Document 1: JP 5852490 (U.S. Pat. No. 9,176,379)-   Patent Document 2: JP-A 2015-180928 (U.S. Pat. No. 9,563,123)-   Patent Document 3: JP-A 2015-172746 (U.S. Pat. No. 9,448,475)

SUMMARY OF INVENTION

As the wavelength of light becomes shorter, the energy density thereofbecomes higher and hence, the number of photons generated upon exposurebecomes smaller. A variation in photon number causes variations in LWRand CDU. As the exposure dose increases, the number of photonsincreases, leading to a less variation of photon number. Thus there is atradeoff relationship between sensitivity and resolution, LWR and CDU.In particular, the EUV lithography resist materials have the tendencythat a lower sensitivity leads to better LWR and CDU.

An increase in acid diffusion also causes degradation of resolution, LWRand CDU. This is because acid diffusion not only causes image blur, butalso proceeds non-uniformly in a resist film. For suppressing aciddiffusion, it is effective to lower the PEB temperature, to use a bulkyacid which is least diffusive, or to increase the amount of quencheradded. However, any of these means for reducing acid diffusion resultsin a lowering of sensitivity. Either the means for reducing photonvariation or the means for reducing acid diffusion variation leads to alowering of resist sensitivity.

An object of the invention is to provide a chemically amplified resistcomposition which exerts a high sensitizing effect and an acid diffusionsuppressing effect and has improved resolution, LWR and CDU, and apattern forming process using the same.

A significant increase of acid generation efficiency and a significantsuppression of acid diffusion must be achieved before the tradeoffrelationship between sensitivity and resolution, LWR and CDU can beovercome.

Iodine is substantially absorptive to EUV of wavelength 13.5 nm and EBbecause of its high atomic number, and releases many secondary electronsupon exposure because of many electron orbits in its molecule. Thesecondary electrons thus released provide energy transfer to an acidgenerator, achieving a high sensitizing effect.

The inventors have found that when a quaternary ammonium salt selectedfrom a quaternary ammonium iodide, quaternary ammonium dibromoiodide,quaternary ammonium bromodiiodide, and quaternary ammonium triiodide isadded as the quencher to a chemically amplified resist compositioncomprising an acid generator, the resulting resist composition forms aresist film which exerts a high sensitizing effect and an acid diffusionsuppressing effect, experiences no film thickness loss afterdevelopment, and has a high sensitivity, minimized LWR and improved CDU.

In one aspect, the invention provides a chemically amplified resistcomposition comprising a quencher containing a quaternary ammonium saltselected from the group consisting of a quaternary ammonium iodide,quaternary ammonium dibromoiodide, quaternary ammonium bromodiiodide,and quaternary ammonium triiodide, and an acid generator.

In one preferred embodiment, the quaternary ammonium salt has theformula (1) or (2).

Herein R¹ to R⁴ and R⁵ to R¹⁰ are each independently a C₁-C₂₄ straight,branched or cyclic alkyl group, C₂-C₂₄ straight, branched or cyclicalkenyl group, C₂-C₂₄ straight, branched or cyclic alkynyl group, orC₆-C₂₄ aryl group, which may contain a halogen, hydroxyl, carboxyl,ether, ester, thiol, thioester, thionoester, dithioester, amino, nitro,sulfone or ferrocenyl moiety, a pair of R¹ and R², R¹ and R⁴, R² and R³,and/or R³ and R⁴ may bond together to form a ring, or a pair of R¹ andR², R¹ and R⁴, R² and R⁴, or R³ and R⁴, taken together, may form adouble bond, R¹¹ is a C₂-C₁₂ straight, branched or cyclic alkylene groupwhich may contain an ether and/or ester moiety, X⁻ is an anion selectedfrom the group consisting of I⁻, Br₂I⁻, BrI₂ ⁻ and I₃ ⁻.

In one preferred embodiment, the acid generator is capable of generatingsulfonic acid, imidic acid or methide acid.

The resist composition may further comprise a base polymer.

In owe preferred embodiment, the base polymer comprises recurring unitsof at least one type selected from recurring units having the formulae(f1) to (f3).

Herein R^(A) is each independently hydrogen or methyl. Z¹ is a singlebond, phenylene, —O—Z¹¹—, or —C(═O)—Z¹²—Z¹¹—, Z¹¹ is a C₁-C₆ straight,branched or cyclic alkylene group or C₂-C₆ straight, branched or cyclicalkenylene group which may contain a carbonyl, ester, ether or hydroxylmoiety, or phenylene group, Z¹² is —O— or —NH—. R⁵¹, R⁵², R⁵³, R⁵⁴, R⁵⁵,R⁵⁶, R⁵⁷, and R⁵⁸ are each independently a C₁-C₁₂ straight, branched orcyclic alkyl group which may contain a carbonyl, ester or ether moiety,or a C₆-C₁₂ aryl, C₇-C₂₀ aralkyl, or mercaptophenyl group. Z² is asingle bond, —Z²¹—C(O)O—, —Z²¹—O—, or —Z²¹—O—C(═O)—, Z²¹ is a C₁-C₁₂straight, branched or cyclic alkylene group which may contain acarbonyl, ester or ether moiety. Z³ is a single bond, methylene,ethylene, phenylene, fluorinated phenylene, —O—Z³¹—, or —C(═O)—Z³²—Z³¹—,Z³¹ is a C₁-C₆ straight, branched or cyclic alkylene group or C₂-C₆straight, branched or cyclic alkenylene group which may contain acarbonyl, ester, ether or hydroxyl moiety, or a phenylene, fluorinatedphenylene or trifluoromethyl-substituted phenylene group, Z³² is —O— or—NH—. A¹ is hydrogen or trifluoromethyl, and M⁻ is a non-nucleophiliccounter ion.

In one preferred embodiment, the acid generator also functions as a basepolymer. In this case, the acid generator is a polymer comprisingrecurring units of at least one type selected from recurring unitshaving the formulae (f1) to (f3) defined above.

In one preferred embodiment, the base polymer comprises recurring unitshaving the formula (a1) or recurring units having the formula (a2).

Herein R^(A) is each independently hydrogen or methyl, R¹¹ and R¹² areeach independently an acid labile group, X¹ is a single bond, phenylene,naphthylene, or a C₁-C₁₂ linking group containing ester moiety orlactone ring, and X² is a single bond or ester group.

In one preferred embodiment, the resist composition is a chemicallyamplified positive resist composition.

In another preferred embodiment, the resist composition is a chemicallyamplified negative resist composition. In this case, the base polymer isan acid labile group-free polymer.

In either embodiment, the resist composition may further comprise anorganic solvent and/or a surfactant.

In another aspect, the invention provides a pattern forming processcomprising the steps of coating the resist composition defined aboveonto a substrate, baking, exposing the resulting resist film tohigh-energy radiation, and developing the resist film with a developer.

Preferably, the high-energy radiation is ArF excimer laser of wavelength193 nm, KrF excimer laser of wavelength 248 nm, EB, or EUV of wavelength3 to 15 nm.

Advantageous Effects of Invention

Since the quaternary ammonium salt defined herein contains an iodineatom featuring substantial light absorption, a resist film containingthe quaternary ammonium salt as a quencher exhibits a sensitizing effectdue to secondary electrons released therefrom upon exposure. Inaddition, the iodine-containing resist film exerts an acid diffusionsuppressing effect and a high dissolution contrast. Thus the resist filmexhibits high resolution, high sensitivity, minimal LWR, and ImprovedCDU as a positive or negative resist film subject to alkalinedevelopment or as a negative resist film subject to organic solventdevelopment.

DESCRIPTION OF EMBODIMENTS

As used herein, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. The notation(Cn-Cm) means a group containing from n to m carbon atoms per group. Mestands for methyl, Ac for acetyl, and Ph for phenyl.

The abbreviations and acronyms have the following meaning.

EB: electron beam

EUV: extreme ultraviolet

Mw: weight average molecular weight

Mn: number average molecular weight

Mw/Mn: molecular weight distribution or dispersity

GPC: gel permeation chromatography

PEB: post-exposure bake

PAG: photoacid generator

LWR: line width roughness

CDU: critical dimension uniformity

Chemically Amplified Resist Composition

The chemically amplified resist composition of the invention is definedas comprising a quencher containing a quaternary ammonium salt selectedfrom among a quaternary ammonium iodide, quaternary ammoniumdibromoiodide, quaternary ammonium bromodiiodide, and quaternaryammonium triiodide, and an acid generator. The quaternary ammonium saltundergoes ion exchange with an acid generated from the acid generator toform an iodonium salt and release hydriodic acid. The quaternaryammonium salt has an acid trapping ability and an acid diffusionsuppressing effect.

The acid diffusion suppressing effect and contrast enhancing effect ofthe quaternary ammonium salt are valid in both the positive or negativepattern formation by alkaline development and the negative patternformation by organic solvent development.

Quencher

The quencher in the chemically amplified resist composition contains aquaternary ammonium salt selected from the group consisting of aquaternary ammonium iodide, quaternary ammonium dibromoiodide,quaternary ammonium bromodiiodide, and quaternary ammonium triiodide.The preferred quaternary ammonium salt has the formula (1) or (2).

Herein R¹ to R⁴ and R⁵ to R¹⁰ are each independently a C₁-C₂₄ straight,branched or cyclic alkyl group, C₂-C₂₄ straight, branched or cyclicalkenyl group, C₂-C₂₄ straight, branched or cyclic alkynyl group, orC₆-C₂₄ aryl group, which may contain a halogen, hydroxyl, carboxyl,ether, ester, thiol, thioester, thionoester, dithioester, amino, nitro,sulfone or ferrocenyl moiety. A pair of R¹ and R², R¹ and R⁴, R² and R³,and/or R³ and R⁴ may bond together to form a ring, or a pair of R¹ andR², R¹ and R⁴, R² and R³, or R³ and R⁴, taken together, may form adouble bond. R¹¹ is a C₂-C₁₂ straight, branched or cyclic alkylene groupwhich may contain an ether and/or ester moiety. X⁻ is an anion selectedfrom the group consisting of I⁻, Br₂I⁻, BrI₂ ⁻ and I₃ ⁻.

Examples of the cation moiety in the quaternary ammonium salt of formula(1) are given below, but not limited thereto.

Examples of the cation moiety in the quaternary ammonium salt of formula(2) are given below, but not limited thereto.

Since the quaternary ammonium salt contains an iodine atom or atoms inthe molecule, it has substantial EUV absorption. Upon EUV exposure, itgenerates secondary electrons, followed by energy transfer to an acidgenerator, leading to sensitization. This establishes a high sensitivityand low acid diffusion, succeeding in improving both LWR or CDU andsensitivity.

The quaternary ammonium salt may be synthesized, for example, byneutralization reaction of a quaternary ammonium hydroxide withhydriodic acid. Also commercially available products are useful as thequaternary ammonium salt.

From the standpoints of sensitivity and acid diffusion suppressingeffect, the quaternary ammonium salt is preferably present in the resistcomposition in an amount of 0.001 to 50 parts, more preferably 0.01 to20 parts by weight per 100 parts by weight of the base polymer to bedescribed below.

The quencher may contain a quencher other than the quaternary ammoniumsalt. The other quencher is typically selected from conventional basiccompounds. Conventional basic compounds include primary, secondary, andtertiary aliphatic amines, mixed amines, aromatic amines, heterocyclicamines, nitrogen-containing compounds with carboxyl group,nitrogen-containing compounds with sulfonyl group, nitrogen-containingcompounds with hydroxyl group, nitrogen-containing compounds withhydroxyphenyl group, alcoholic nitrogen-containing compounds, amidederivatives, imide derivatives, and carbamate derivatives. Also includedare primary, secondary, and tertiary amine compounds, specifically aminecompounds having a hydroxyl, ether, ester, lactone ring, cyano, orsulfonic acid ester group as described in JP-A 2008-111103, paragraphs[0146]-[0164], and compounds having a carbamate group as described in JP3790649. Addition of a basic compound may be effective for furthersuppressing the diffusion rate of acid in the resist film or correctingthe pattern profile.

Quenchers of polymer type as described in U.S. Pat. No. 7,598,016 (JP-A2008-239918) are also useful as the other quencher. The polymericquencher segregates at the resist surface after coating and thusenhances the rectangularity of resist pattern. When a protective film isapplied as is often the case in the immersion lithography, the polymericquencher is also effective for preventing a film thickness loss ofresist pattern or rounding of pattern top.

Also, an ammonium salt, sulfonium salt or iodonium salt may be added asthe other quencher. Suitable ammonium salts, sulfonium salts andiodonium salts added as the other quencher are salts with carboxylicadd, sulfonic acid, sulfonimide and saccharin. The carboxylic acid usedherein may or may not be fluorinated at α-position.

The other quencher is preferably added in an amount of 0 to 5 parts,more preferably 0 to 4 parts by weight per 100 parts by weight of thebase polymer.

Acid Generator

The chemically amplified resist composition contains an acid generator.The acid generator used herein may be either an acid generator ofaddition type which is different from the quaternary ammonium salt andcomponents to be described later, or an acid generator of polymer typewhich also functions as a base polymer, that is, an acidgenerator-and-base polymer component.

The acid generator of addition type is typically a compound (PAG)capable of generating an acid upon exposure to actinic ray or radiation.Although the PAG used herein may be any compound capable of generatingan acid upon exposure to high-energy radiation, those compounds capableof generating sulfonic acid, sulfonimide or sulfonmethide are preferred.Suitable PAGs include sulfonium salts, iodonium salts,sulfonyldiazomethane, N-sulfonyloxyimide, and oxime-O-sulfonate acidgenerators. Exemplary PAGs are described in JP-A 2008-111103, paragraphs[0122]-[0142] (U.S. Pat. No. 7,537,880).

As the PAG, compounds having the formula (A) are also preferably used.

In formula (A), R¹⁰¹, R¹⁰² and R¹⁰³ are each independently a C₁-C₂₀straight, branched or cyclic monovalent hydrocarbon group which maycontain a heteroatom, any two of R¹⁰¹, R¹⁰² and R¹⁰³ may bond togetherto form a ring with the sulfur atom to which they are attached.

In formula (A), X⁻ is an anion selected from the formulae (A1) to (A4).

In formula (A1), R^(fa) is fluorine or a C₁-C₄₀ straight, branched orcyclic monovalent hydrocarbon group which may contain a heteroatom.

Of the anions of formula (A1), a structure having formula (A1′) ispreferred.

In formula (A1′), R¹⁰⁴ is hydrogen or trifluoromethyl, preferablytrifluoromethyl. R¹⁰⁵ is a C₁-C₃₈ straight, branched or cyclicmonovalent hydrocarbon group which may contain a heteroatom. Suitableheteroatoms include oxygen, nitrogen, sulfur and halogen, with oxygenbeing preferred. Of the monovalent hydrocarbon groups, those of 6 to 30carbon atoms are preferred because a high resolution is available infine pattern formation. Suitable monovalent hydrocarbon groups includemethyl, ethyl, propyl, isopropyl, butyl, isobutyl, s-butyl, t-butyl,pentyl, neopentyl, cyclopentyl, hexyl, cyclohexyl, 3-cyclohexenyl,heptyl, 2-ethylhexyl, nonyl, undecyl, tridecyl, pentadecyl, heptadecyl,1-adamantyl, 2-adamantyl, 1-adamantylmethyl, norbornyl, norbornylmethyl,tricyclodecanyl, tetracyclododecanyl, tetracyclododecanylmethyl,dicyclohexylmethyl, icosanyl, allyl, benzyl, diphenylmethyl,tetrahydrofuryl, methoxymethyl, ethoxymethyl, methylthiomethyl,acetamidomethyl, trifluoroethyl, (2-methoxyethoxy)methyl, acetoxymethyl,2-carboxy-1-cyclohexyl, 2-oxopropyl, 4-oxo-1-adamantyl, and3-oxocyclohexyl. Also included are the foregoing groups in which atleast one hydrogen is replaced by a radical containing a heteroatom suchas oxygen, sulfur, nitrogen or halogen, or in which at least one carbonatom is replaced by a radical containing a heteroatom such as oxygen,sulfur or nitrogen, so that the group may contain a hydroxyl, cyano,carbonyl, ether, ester, sulfonic acid ester, carbonate, lactone ring,sultone ring, carboxylic acid anhydride or haloalkyl radical.

With respect to the synthesis of the sulfonium salt having an anion offormula (A1′), reference is made to JP-A 2007-145797, JP-A 2008-106045,JP-A 2009-007327, and JP-A 2009-258695. Also useful are the sulfoniumsalts described in JP-A 2010-215608, JP-A 2012-041320, JP-A 2012-106986,and JP-A 2012-153644.

Examples of the sulfonium salt having an anion of formula (A1) are shownbelow, but not limited thereto.

In formula (A2), R^(fb1) and R^(fb2) are each independently fluorine ora C₁-C₄₀ straight, branched or cyclic monovalent hydrocarbon group whichmay contains a heteroatom. Suitable monovalent hydrocarbon groups are asexemplified above for R¹⁰⁵. Preferably R^(fb1) and R^(fb2) each arefluorine or a straight C₁-C₄ fluorinated alkyl group. A pair of R^(fb1)and R^(fb2) may bond together to form a ring with the linkage(—CF₂—SO₂—N⁻—SO₂—CF₂—) to which they are attached, and preferably thepair is a fluorinated ethylene or fluorinated propylene group to form aring structure.

In formula (A3), R^(fc1), R^(fc2) and R^(fc3) are each independentlyfluorine or a C₁-C₄₀ straight, branched or cyclic monovalent hydrocarbongroup which may contain a heteroatom. Suitable monovalent hydrocarbongroups are as exemplified above for R¹⁰⁵. Preferably R^(fc1), R^(fc2)and R^(fc3) each are fluorine or a straight C₁-C₄ fluorinated alkylgroup. A pair of R^(fc1) and R^(fc2) may bond together to form a ringwith the linkage (—CF₂—SO₂—C⁻—SO₂—CF₂—) to which they are attached, andpreferably the pair is a fluorinated ethylene or fluorinated propylenegroup to form a ring structure.

In formula (A4), R^(fd) is a C₁-C₄₀ straight, branched or cyclicmonovalent hydrocarbon group which may contain a heteroatom. Suitablemonovalent hydrocarbon groups are as exemplified above for R¹⁰⁵.

With respect to the synthesis of the sulfonium salt having an anion offormula (A4), reference is made to JP-A 2010-215608 and JP-A2014-133723.

Examples of the sulfonium salt having an anion of formula (A4) are shownbelow, but not limited thereto.

The compound having the anion of formula (A4) has a sufficient acidstrength to cleave acid labile groups in the base polymer because it isfree of fluorine at α-position of sulfo group, but has twotrifluoromethyl groups at β-position. Thus the compound is a useful PAG.

Also compounds having the formula (B) are useful as the PAG.

In formula (B), R²⁰¹ and R²⁰² are each independently a C₁-C₃₀ straight,branched or cyclic monovalent hydrocarbon group which may contain aheteroatom. R²⁰³ is a C₁-C₃₀ straight, branched or cyclic divalenthydrocarbon group which may contain a heteroatom. Any two of R²⁰¹, R²⁰²and R²⁰³ may bond together to form a ring with the sulfur atom to whichthey are attached. L^(A) is a single bond, ether group or a straight,branched or cyclic C₁-C₂₀ divalent hydrocarbon group which may contain aheteroatom. X^(A), X^(B), X^(C) and X^(D) are each independentlyhydrogen, fluorine or trifluoromethyl, with the proviso that at leastone of X^(A), X^(B), X^(C) and X^(D) is fluorine or trifluoromethyl, andk is an integer of 0 to 3.

Suitable monovalent hydrocarbon groups include methyl, ethyl, propyl,isopropyl, n-butyl, s-butyl, t-butyl, n-pentyl, t-pentyl, n-hexyl,n-octyl, n-nonyl, n-decyl, cyclopentyl, cyclohexyl, 2-ethylhexyl,cyclopentylmethyl, cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl,cyclohexylethyl, cyclohexylbutyl, norbornyl, oxanorbornyl,tricyclo[5.2.1.0^(2,6)]decanyl, adamantyl, phenyl, naphthyl andanthracenyl. Also included are the foregoing groups in which at leastone hydrogen is replaced by a radical containing a heteroatom such asoxygen, sulfur, nitrogen or halogen, or in which at least one carbon isreplaced by a radical containing a heteroatom such as oxygen, sulfur ornitrogen, so that the group may contain a hydroxyl, cyano, carbonyl,ether, ester, sulfonic acid ester, carbonate, lactone ring, sultonering, carboxylic acid anhydride or haloalkyl radical.

Suitable divalent hydrocarbon groups include linear alkane diyl groupssuch as methylene, ethylene, propane-1,3-diyl, butane-1,4-diyl,pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl,nonane-1,9-diyl, decane-1,10-diyl, undecane-1,11-diyl,dodecane-1,12-diyl, tridecane-1,13-diyl, tetradecane-1,14-diyl,pentadecane-1,15-diyl, hexadecane-1,16-diyl, heptadecane-1,17-diyl;saturated cyclic divalent hydrocarbon groups such as cyclopentanediyl,cyclohexanediyl, norbornanediyl, and adamantanediyl; and unsaturatedcyclic divalent hydrocarbon groups such as phenylene and naphthylene.Also included are the foregoing groups in which at least one hydrogenatom is replaced by an alkyl group such as methyl, ethyl, propyl,n-butyl or t-butyl, or in which at least one hydrogen atom is replacedby a radical containing a heteroatom such as oxygen, sulfur, nitrogen orhalogen, or in which at least one carbon atom is replaced by a radicalcontaining a heteroatom such as oxygen, sulfur or nitrogen, so that thegroup may contain a hydroxyl, cyano, carbonyl, ether, ester, sulfonicacid ester, carbonate, lactone ring, sultone ring, carboxylic acidanhydride or haloalkyl radical. Suitable heteroatoms include oxygen,nitrogen, sulfur and halogen, with oxygen being preferred.

Of the PAGs having formula (B), those having formula (B′) are preferred.

In formula (B′), L^(A) is as defined above. R is hydrogen ortrifluoromethyl, preferably trifluoromethyl. R³⁰¹, R³⁰² and R³⁰³ areeach independently hydrogen or a C₁-C₂₀ straight, branched or cyclicmonovalent hydrocarbon group which may contain a heteroatom. Suitablemonovalent hydrocarbon groups are as exemplified above for R¹⁰⁵. Thesubscripts x and y each are an integer of 0 to 5, and z is an integer of0 to 4.

Examples of the PAG having formula (B) are shown below, but not limitedthereto. Herein R is as defined above.

Of the foregoing PAGs, those compounds having an anion of formula (A1′)or (A4) are especially preferred because of reduced acid diffusion andhigh solubility in resist solvent, and those compounds having an anionof formula (B′) are especially preferred because of minimized aciddiffusion.

An appropriate amount of the acid generator of addition type is 0.1 to50 parts, more preferably 1 to 40 parts by weight per 100 parts byweight of the base polymer.

In case the acid generator is an acid generator-and-base polymer, thisacid generator is a polymer, preferably comprising recurring unitsderived from a compound capable of generating an acid in response toactinic light or radiation. In this case, the acid generator ispreferably a base polymer to be described below, specifically comprisingrecurring units (f) as essential unit.

Base Polymer

In the case of a positive resist composition, the base polymer in theresist composition is a polymer comprising acid labile group-containingrecurring units. The acid labile group-containing recurring units arepreferably recurring units having the formula (a1) or recurring unitshaving the formula (a2). Sometimes these recurring units are simplyreferred to as recurring units (a1) and (a2).

Herein R^(A) is each independently hydrogen or methyl. R²¹ and R²² areeach independently an acid labile group. X¹ is a single bond, phenylene,naphthylene, or a C₁-C₁₂ linking group containing ester moiety orlactone ring. X² is a single bond or ester group.

Examples of the recurring units (a1) are shown below, but not limitedthereto. Herein R^(A) and R²¹ are as defined above.

The acid labile groups represented by R²¹ and R²² in the recurring units(a1) and (a2) may be selected from a variety of such groups, forexample, those groups described in JP-A 2013-080033 (U.S. Pat. No.8,574,817) and JP-A 2013-083821 (U.S. Pat. No. 8,846,303).

Typical of the acid labile group are groups of the following formulae(AL-1) to (AL-3).

In formulae (AL-1) and (AL-2), R²³ and R²⁶ are each independently amonovalent hydrocarbon group of 1 to 40 carbon atoms, preferably 1 to 20carbon atoms, typically straight, branched or cyclic alkyl, which maycontain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. R²⁴and R²⁵ are each independently hydrogen or a monovalent hydrocarbongroup of 1 to 20 carbon atoms, typically straight, branched or cyclicalkyl, which may contain a heteroatom such as oxygen, sulfur, nitrogenor fluorine. The subscript “a” is an integer of 0 to 10, especially 1 to5. A pair of R²⁴ and R²⁵, R²⁴ and R²⁶, or R²⁵ and R²⁶ may bond togetherto form a ring, typically alicyclic, with the carbon atom or carbon andoxygen atoms to which they are attached, the ring containing 3 to 20carbon atoms, preferably 4 to 16 carbon atoms.

In formula (AL-3), R²⁷, R²⁸ and R²⁹ are each independently a monovalenthydrocarbon group of 1 to 20 carbon atoms, typically straight, branchedor cyclic alkyl, which may contain a heteroatom such as oxygen, sulfur,nitrogen or fluorine. A pair of R²⁷ and R²⁸, R²⁷ and R²⁹, or R²⁸ and R²⁹may bond together to form a ring, typically alicyclic, with the carbonatom to which they are attached, the ring containing 3 to 20 carbonatoms, preferably 4 to 16 carbon atoms.

The base polymer may further comprise recurring units (b) having aphenolic hydroxyl group as an adhesive group. Examples of suitablemonomers from which recurring units (b) are derived are given below, butnot limited thereto. Herein R^(A) is as defined above.

Further, recurring units (c) having another adhesive group selected fromhydroxyl (other than the foregoing phenolic hydroxyl), lactone ring,ether, ester, carbonyl and cyano groups may also be incorporated in thebase polymer. Examples of suitable monomers from which recurring units(c) are derived are given below, but not limited thereto. Herein R^(A)is as defined above.

In the case of a monomer having a hydroxyl group, the hydroxyl group maybe replaced by an acetal group susceptible to deprotection with acid,typically ethoxyethoxy, prior to polymerization, and the polymerizationbe followed by deprotection with weak acid and water. Alternatively, thehydroxyl group may be replaced by an acetyl, formyl, pivaloyl or similargroup prior to polymerization, and the polymerization be followed byalkaline hydrolysis.

In another preferred embodiment, the base polymer may further compriserecurring units (d) selected from units of indene, benzofuran,benzothiophene, acenaphthylene, chromone, coumarin, and norbornadiene,or derivatives thereof. Suitable monomers are exemplified below.

Besides the recurring units described above, further recurring units (e)which are derived from styrene, vinylnaphthalene, vinylanthracene,vinylpyrene, methyleneindene, vinylpyridine, and vinylcarbazole may beincorporated in the base polymer.

In a further embodiment, recurring units (f) derived from an onium salthaving a polymerizable carbon-carbon double bond may be incorporated inthe base polymer. JP-A 2005-084365 discloses sulfonium and iodoniumsalts having a polymerizable carbon-carbon double bond capable ofgenerating a sulfonic acid. JP-A 2006-178317 discloses a sulfonium salthaving sulfonic acid directly attached to the main chain.

The preferred recurring units (f) include recurring units having formula(f1), recurring units having formula (f2), and recurring units havingformula (f3). These units are simply referred to as recurring units(f1), (f2) and (f3), which may be used alone or in combination of two ormore types.

Herein R^(A) is each independently hydrogen or methyl. Z¹ is a singlebond, phenylene, —O—Z¹¹—, or —C(═O)—Z¹²—Z¹¹—, wherein Z¹¹ is a straight,branched or cyclic C₁-C₆ alkylene group or straight, branched or cyclicC₂-C₆ alkenylene group which may contain a carbonyl, ester, ether orhydroxyl moiety, or phenylene group, Z¹² is —O— or —NH—. R⁵¹, R⁵², R⁵³,R⁵⁴, R⁵⁵, R⁶⁶, R⁵⁷, and R⁵⁸ are each independently a straight, branchedor cyclic C₁-C₁₂ alkyl group which may contain a carbonyl, ester orether moiety, or a C₆-C₁₂ aryl, C₇-C₂₀ aralkyl, or mercaptophenyl group.Z² is a single bond, —Z²¹—C(═O)—O—, —Z²¹—O—, or —Z²¹—O—C(═O)—, whereinZ²¹ is a straight, branched or cyclic C₁-C₁₂ alkylene group which maycontain a carbonyl, ester or ether moiety. Z³ is a single bond,methylene, ethylene, phenylene, fluorinated phenylene, —O—Z³¹—, or—C(═O)—Z³²—Z³¹—, wherein Z³¹ is a straight, branched or cyclic C₁-C₆alkylene group or straight, branched or cyclic C₂-C₆ alkenylene groupwhich may contain a carbonyl, ester, ether or hydroxyl moiety, or aphenylene, fluorinated phenylene or trifluoromethyl-substitutedphenylene group, Z³² is —O— or —NH—. A¹ is hydrogen or trifluoromethyl.M⁻ is a non-nucleophilic counter ion.

Examples of the monomer from which recurring unit (f1) is derived areshown below, but not limited thereto. R^(A) and M⁻ are as defined above.

Examples of the non-nucleophilic counter ion M⁻ include halide ions suchas chloride and bromide ions; fluoroalkylsulfonate ions such astriflate, 1,1,1-trifluoroethanesulfonate, and nonafluorobutanesulfonateions; arylsulfonate ions such as tosylate, benzenesulfonate,4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonateions; alkylsulfonate ions such as mesylate and butanesulfonate ions;sulfonimide ions such as bis(trifluoromethylsulfonyl)imide,bis(perfluoroethylsulfonyl)imide and bis(perfluorobutylsulfonyl)imideions; sulfonmethide ions such as tris(trifluoromethylsulfonyl)methideand tris(perfluoroethylsulfonyl)methide ions.

Also included are sulfonates having fluorine substituted at α-positionas represented by the formula (K-1) and sulfonates having fluorinesubstituted at α- and β-positions as represented by the formula (K-2).

In formula (K-1), R⁶¹ is hydrogen, or a C₁-C₂₀ straight, branched orcyclic alkyl group, C₂-C₂₀ straight, branched or cyclic alkenyl group,or C₆-C₂₀ aryl group, which may contain an ether, ester, carbonylmoiety, lactone ring, or fluorine atom. In formula (K-2), R⁶² ishydrogen, or a C₁-C₃₀ straight, branched or cyclic alkyl group, C₂-C₃₀straight, branched or cyclic acyl group, C₂-C₂₀ straight, branched orcyclic alkenyl group, C₆-C₂₀ aryl group or C₆-C₂₀ aryloxy group, whichmay contain an ether, ester, carbonyl moiety or lactone ring.

Examples of the monomer from which recurring unit (f2) is derived areshown below, but not limited thereto. R^(A) is as defined above.

Examples of the monomer from which recurring unit (f3) is derived areshown below, but not limited thereto. R^(A) is as defined above.

The attachment of an acid generator to the polymer main chain iseffective in restraining acid diffusion, thereby preventing a reductionof resolution due to blur by acid diffusion. Also edge roughness isImproved since the acid generator is uniformly distributed.

The base polymer comprising recurring units (f) also functions as theacid generator. Since this base polymer is integrated with the acidgenerator, an acid generator of addition type may or may not be added tothe chemically amplified resist composition.

The base polymer for formulating the positive resist compositioncomprises recurring units (a1) or (a2) having an acid labile group asessential component and additional recurring units (b), (c), (d), (e),and (f) as optional components. A fraction of units (a1), (a2), (b),(c), (d), (e), and (f) is: preferably 0≤a1<1.0, 0≤a2<1.0, 0<a1+a2<1.0,0≤b≤0.9, 0≤c≤0.9, 0≤d≤0.8, 0≤e≤0.8, and 0≤f≤0.5; more preferably0≤a1≤0.9, 0≤a2≤0.9, 0.1≤a1+a2≤0.9, 0≤b≤0.8, 0≤c≤0.8, 0≤d≤0.7, 0≤c≤0.7,and 0≤f≤0.4; and even more preferably 0≤a1≤0.8, 0≤a2≤0.8, 0.1≤a1+a2≤0.8,0≤b≤0.75, 0≤c≤0.75, 0≤d≤0.6, 0≤e≤0.6, and 0≤f≤0.3. In the embodimentwherein the base polymer also functions as an acid generator, thefraction of recurring units (f) is preferably 0<f≤0.5, more preferably0.01≤f≤0.4, and even more preferably 0.02≤f≤0.3. Notably, f=f1+f2+f3,meaning that unit (f) is at least one of units (f1) to (f3), anda1+a2+b+c+d+e+f=1.0.

For the base polymer for formulating the negative resist composition, anacid labile group is not necessarily essential. The base polymercomprises recurring units (b), and optionally recurring units (c), (d),(e), and/or (f). A fraction of these units is: preferably 0<b≤1.0,0≤c≤0.9, 0≤d≤0.8, 0≤e≤0.8, and 0≤f≤0.5; more preferably 0.2≤b≤1.0,0≤c≤0.8, 0≤d≤0.7, 0≤e≤0.7, and 0≤f≤0.4; and even more preferably0.3≤b≤1.0, 0≤c≤0.75, 0≤d≤0.6, 0≤e≤0.6, and 0≤f≤0.3. In the embodimentwherein the base polymer also functions as an acid generator, thefraction of recurring units (f) is preferably 0<f≤0.5, more preferably0.01≤f≤0.4, and even more preferably 0.02≤f≤0.3. Notably, f=f1+f2+f3,meaning that unit (f) is at least one of units (f1) to (f3), andb+c+d+e+f=1.0.

The base polymer may be synthesized by any desired methods, for example,by dissolving one or more monomers selected from the monomerscorresponding to the foregoing recurring units in an organic solvent,adding a radical polymerization initiator thereto, and effecting heatpolymerization. Examples of the organic solvent which can be used forpolymerization include toluene, benzene, tetrahydrofuran, diethyl ether,and dioxane. Examples of the polymerization initiator used hereininclude 2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the system is heated at 50 to 80° C. for polymerization totake place. The reaction time is preferably 2 to 100 hours, morepreferably 5 to 20 hours.

When hydroxystyrene or hydroxyvinylnaphthalene is copolymerized, analternative method is possible. Specifically, acetoxystyrene oracetoxyvinylnaphthalene is used instead of hydroxystyrene orhydroxyvinylnaphthalene, and after polymerization, the acetoxy group isdeprotected by alkaline hydrolysis, for thereby converting the polymerproduct to hydroxystyrene or hydroxyvinylnaphthalene. For alkalinehydrolysis, a base such as aqueous ammonia or triethylamine may be used.Preferably the reaction temperature is −20° C. to 100° C., morepreferably 0° C. to 60° C., and the reaction time is 0.2 to 100 hours,more preferably 0.5 to 20 hours.

The base polymer should preferably have a weight average molecularweight (Mw) in the range of 1,000 to 500,000, and more preferably 2,000to 30,000, as measured by GPC versus polystyrene standards usingtetrahydrofuran (THF) solvent. With too low a Mw, the resist compositionmay become less heat resistant. A polymer with too high a Mw may losealkaline solubility and give rise to a footing phenomenon after patternformation.

If a base polymer has a wide molecular weight distribution or dispersity(Mw/Mn), which indicates the presence of lower and higher molecularweight polymer fractions, there is a possibility that foreign matter isleft on the pattern or the pattern profile is degraded. The influencesof molecular weight and dispersity become stronger as the pattern rulebecomes finer. Therefore, the base polymer should preferably have anarrow dispersity (Mw/Mn) of 1.0 to 2.0, especially 1.0 to 1.5, in orderto provide a resist composition suitable for micropatterning to a smallfeature size.

It is understood that a blend of two or more polymers which differ incompositional ratio, Mw or Mw/Mn is acceptable.

Other Components

With the foregoing components, other components such as an organicsolvent, surfactant, dissolution inhibitor, and crosslinker may beblended in any desired combination to formulate a chemically amplifiedpositive or negative resist composition. This positive or negativeresist composition has a very high sensitivity in that the dissolutionrate in developer of the base polymer in exposed areas is accelerated bycatalytic reaction. In addition, the resist film has a high dissolutioncontrast, resolution, exposure latitude, and process adaptability, andprovides a good pattern profile after exposure, and minimal proximitybias because of restrained acid diffusion. By virtue of theseadvantages, the composition is fully useful in commercial applicationand suited as a pattern-forming material for the fabrication of VLSIs.Particularly when an acid generator is incorporated to formulate achemically amplified positive resist composition capable of utilizingacid catalyzed reaction, the composition has a higher sensitivity and isfurther improved in the properties described above.

In the case of positive resist compositions, inclusion of a dissolutioninhibitor may lead to an increased difference in dissolution ratebetween exposed and unexposed areas and a further improvement inresolution. In the case of negative resist compositions, a negativepattern may be formed by adding a crosslinker to reduce the dissolutionrate of exposed area.

Examples of the organic solvent used herein are described in JP-A2008-111103, paragraphs [0144]-[0145] (U.S. Pat. No. 7,537,880).Exemplary solvents include ketones such as cyclohexanone, cyclopentanoneand methyl-2-n-pentyl ketone; alcohols such as 3-methoxybutanol,3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether,ethylene glycol monomethyl ether, propylene glycol monoethyl ether,ethylene glycol monoethyl ether, propylene glycol dimethyl ether, anddiethylene glycol dimethyl ether, esters such as propylene glycolmonomethyl ether acetate (PGMEA), propylene glycol monoethyl etheracetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl3-methoxypropionate, ethyl 3-ethoxypropionate, t-butyl acetate, t-butylpropionate, and propylene glycol mono-t-butyl ether acetate; andlactones such as γ-butyrolactone, which may be used alone or inadmixture.

The organic solvent is preferably added in an amount of 100 to 10,000parts, and more preferably 200 to 8,000 parts by weight per 100 parts byweight of the base polymer.

Exemplary surfactants are described in JP-A 2008-111103, paragraphs[0165]-[0166]. Inclusion of a surfactant may improve or control thecoating characteristics of the resist composition. The surfactant ispreferably added in an amount of 0.0001 to 10 parts by weight per 100parts by weight of the base polymer.

The dissolution inhibitor which can be used herein is a compound havingat least two phenolic hydroxyl groups on the molecule, in which anaverage of from 0 to 100 mol % of all the hydrogen atoms on the phenolichydroxyl groups are replaced by acid labile groups or a compound havingat least one carboxyl group on the molecule, in which an average of 50to 100 mol % of all the hydrogen atoms on the carboxyl groups arereplaced by acid labile groups, both the compounds having a molecularweight of 100 to 1,000, and preferably 150 to 800. Typical are bisphenolA, trisphenol, phenolphthalein, cresol novolac, naphthalenecarboxylicacid, adamantanecarboxylic acid, and cholic acid derivatives in whichthe hydrogen atom on the hydroxyl or carboxyl group is replaced by anacid labile group, as described in U.S. Pat. No. 7,771,914 (JP-A2008-122932, paragraphs [0155]-[0178]).

In the positive resist composition, the dissolution inhibitor ispreferably added in an amount of 0 to 50 parts, more preferably 5 to 40parts by weight per 100 parts by weight of the base polymer.

Suitable crosslinkers which can be used herein include epoxy compounds,melamine compounds, guanamine compounds, glycoluril compounds and ureacompounds having substituted thereon at least one group selected fromamong methylol, alkoxymethyl and acyloxymethyl groups, isocyanatecompounds, azide compounds, and compounds having a double bond such asan alkenyl ether group. These compounds may be used as an additive orIntroduced into a polymer side chain as a pendant. Hydroxy-containingcompounds may also be used as the crosslinker.

Of the foregoing crosslinkers, examples of suitable epoxy compoundsinclude tris(2,3-epoxypropyl) isocyanurate, trimethylolmethanetriglycidyl ether, trimethylolpropane triglycidyl ether, andtriethylolethane triglycidyl ether. Examples of the melamine compoundinclude hexamethylol melamine, hexamethoxymethyl melamine, hexamethylolmelamine compounds having 1 to 6 methylol groups methoxymethylated andmixtures thereof, hexamethoxyethyl melamine, hexaacyloxymethyl melamine,hexamethylol melamine compounds having 1 to 6 methylol groupsacyloxymethylated and mixtures thereof. Examples of the guanaminecompound include tetramethylol guanamine, tetramethoxymethyl guanamine,tetramethylol guanamine compounds having 1 to 4 methylol groupsmethoxymethylated and mixtures thereof, tetramethoxyethyl guanamine,tetraacyloxyguanamine, tetramethylol guanamine compounds having 1 to 4methylol groups acyloxymethylated and mixtures thereof. Examples of theglycoluril compound include tetramethylol glycoluril,tetramethoxyglycoluril, tetramethoxymethyl glycoluril, tetramethylolglycoluril compounds having 1 to 4 methylol groups methoxymethylated andmixtures thereof, tetramethylol glycoluril compounds having 1 to 4methylol groups acyloxymethylated and mixtures thereof. Examples of theurea compound include tetramethylol urea, tetramethoxymethyl urea,tetramethylol urea compounds having 1 to 4 methylol groupsmethoxymethylated and mixtures thereof, and tetramethoxyethyl urea.

Suitable isocyanate compounds include tolylene diisocyanate,diphenylmethane diisocyanate, hexamethylene diisocyanate and cyclohexanediisocyanate. Suitable azide compounds include1,1′-biphenyl-4,4′-bisazide, 4,4′-methylidenebisazide, and4,4′-oxybisazide. Examples of the alkenyl ether group-containingcompound include ethylene glycol divinyl ether, triethylene glycoldivinyl ether, 1,2-propanediol divinyl ether, 1,4-butanediol divinylether, tetramethylene glycol divinyl ether, neopentyl glycol divinylether, trimethylol propane trivinyl ether, hexanediol divinyl ether,1,4-cyclohexanediol divinyl ether, pentaerythritol trivinyl ether,pentaerythritol tetravinyl ether, sorbitol tetravinyl ether, sorbitolpentavinyl ether, and trimethylol propane trivinyl ether.

In the negative resist composition, the crosslinker is preferably addedin an amount of 0.1 to 50 parts, more preferably 1 to 40 parts by weightper 100 parts by weight of the base polymer.

To the resist composition, a polymeric additive (or water repellencyimprover) may also be added for improving the water repellency onsurface of a resist film as spin coated. The water repellency improvermay be used in the topcoatless immersion lithography. Suitable waterrepellency improvers include polymers having a fluoroalkyl group andpolymers having a specific structure with a1,1,1,3,3,3-hexafluoro-2-propanol residue and are described in JP-A2007-297590 and JP-A 2008-111103, for example. The water repellencyimprover to be added to the resist composition should be soluble in theorganic solvent as the developer. The water repellency improver ofspecific structure with a 1,1,1,3,3,3-hexafluoro-2-propanol residue iswell soluble in the developer. A polymer having an amino group or aminesalt copolymerized as recurring units may serve as the water repellentadditive and is effective for preventing evaporation of acid during PEB,thus preventing any hole pattern opening failure after development. Anappropriate amount of the water repellency improver is 0 to 20 parts,preferably 0.5 to 10 parts by weight per 100 parts by weight of the basepolymer.

Also, an acetylene alcohol may be blended in the resist composition.Suitable acetylene alcohols are described in JP-A 2008-122932,paragraphs [0179]-[0182]. An appropriate amount of the acetylene alcoholblended is 0 to 5 parts by weight per 100 parts by weight of the basepolymer.

Process

The resist composition is used in the fabrication of various integratedcircuits. Pattern formation using the resist composition may beperformed by well-known lithography processes. The process generallyinvolves coating, prebaking, exposure, and development. If necessary,any additional steps such as PEB may be added.

For example, the chemically amplified resist composition is firstapplied onto a substrate on which an integrated circuit is to be formed(e.g., Si, SiO₂, SiN, SiON, TiN, WSi, BPSG, SOG, or organicantireflective coating) or a substrate on which a mask circuit is to beformed (e.g., Cr, CrO, CrON, MoSi₂, or SiO₂) by a suitable coatingtechnique such as spin coating, roll coating, flow coating, dipping,spraying or doctor coating. The coating is prebaked on a hotplate at atemperature of 60 to 150° C. for 10 seconds to 30 minutes, preferably 80to 120° C. for 30 seconds to 20 minutes. The resulting resist film isgenerally 0.1 to 2 μm thick.

The resist film is then exposed to a desired pattern of high-energyradiation such as UV, deep-UV, EB, EUV, x-ray, soft x-ray, excimer laserlight, γ-ray or synchrotron radiation, directly or through a mask. Theexposure dose is preferably about 1 to 200 mJ/cm², more preferably about10 to 100 mJ/cm², or about 0.1 to 100 μC/cm², more preferably about 0.5to 50 μC/cm². The resist film is further baked (PEB) on a hotplate at 60to 150° C. for 10 seconds to 30 minutes, preferably 80 to 120° C. for 30seconds to 20 minutes.

Thereafter the resist film is developed with a developer in the form ofan aqueous base solution for 3 seconds to 3 minutes, preferably 5seconds to 2 minutes by conventional techniques such as dip, puddle andspray techniques. A typical developer is a 0.1 to 10 wt %, preferably 2to 5 wt % aqueous solution of tetramethylammonium hydroxide (TMAH),tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide(TPAH), or tetrabutylammonium hydroxide (TBAH). The resist film in theexposed area is dissolved in the developer whereas the resist film inthe unexposed area is not dissolved. In this way, the desired positivepattern is formed on the substrate. Inversely in the case of negativeresist, the exposed area of resist film is insolubilized and theunexposed area is dissolved in the developer. It is appreciated that theresist composition of the invention is best suited for micro-patterningusing such high-energy radiation as KrF and ArF excimer laser, BB, EUV,x-ray, soft x-ray, γ-ray and synchrotron radiation.

In an alternative embodiment, a negative pattern may be formed viaorganic solvent development. The developer used herein is preferablyselected from among 2-octanone, 2-nonanone, 2-heptanone, 3-heptanone,4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone,methylcyclohexanone, acetophenone, methylacetophenone, propyl acetate,butyl acetate, isobutyl acetate, pentyl acetate, butenyl acetate,isopentyl acetate, propyl formate, butyl formate, isobutyl formate,pentyl formate, isopentyl formate, methyl valerate, methyl pentenoate,methyl crotonate, ethyl crotonate, methyl propionate, ethyl propionate,ethyl 3-ethoxypropionate, methyl lactate, ethyl lactate, propyl lactate,butyl lactate, isobutyl lactate, pentyl lactate, isopentyl lactate,methyl 2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methylbenzoate, ethyl benzoate, phenyl acetate, benzyl acetate, methylphenylacetate, benzyl formate, phenylethyl formate, methyl3-phenylpropionate, benzyl propionate, ethyl phenylacetate, and2-phenylethyl acetate, and mixtures thereof.

At the end of development, the resist film is rinsed. As the rinsingliquid, a solvent which is miscible with the developer and does notdissolve the resist film is preferred. Suitable solvents includealcohols of 3 to 10 carbon atoms, ether compounds of 8 to 12 carbonatoms, alkanes, alkenes, and alkynes of 6 to 12 carbon atoms, andaromatic solvents. Specifically, suitable alcohols of 3 to 10 carbonatoms include n-propyl alcohol, isopropyl alcohol, 1-butyl alcohol,2-butyl alcohol, isobutyl alcohol, t-butyl alcohol, 1-pentanol,2-pentanol, 3-pentanol, t-pentyl alcohol, neopentyl alcohol,2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol,cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol,3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-ethyl-1-butanol,2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol,3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol,4-methyl-1-pentanol, 4-methyl-2-pentanol, 4-methyl-3-pentanol,cyclohexanol, and 1-octanol. Suitable ether compounds of 8 to 12 carbonatoms include di-n-butyl ether, diisobutyl ether, di-s-butyl ether,di-n-pentyl ether, diisopentyl ether, di-s-pentyl ether, di-t-pentylether, and di-n-hexyl ether. Suitable alkanes of 6 to 12 carbon atomsinclude hexane, heptane, octane, nonane, decane, undecane, dodecane,methylcyclopentane, dimethylcyclopentane, cyclohexane,methylcyclohexane, dimethylcyclohexane, cycloheptane, cyclooctane, andcyclononane. Suitable alkenes of 6 to 12 carbon atoms include hexene,heptene, octene, cyclohexene, methylcyclohexene, dimethylcyclohexene,cycloheptene, and cyclooctene. Suitable alkynes of 6 to 12 carbon atomsinclude hexyne, heptyne, and octyne. Suitable aromatic solvents includetoluene, xylene, ethylbenzene, isopropylbenzene, t-butylbenzene andmesitylene. The solvents may be used alone or in admixture.

Rinsing is effective for minimizing the risk of resist pattern collapseand defect formation. However, rinsing is not essential. If rinsing isomitted, the amount of solvent used may be reduced.

A hole or trench pattern after development may be shrunk by the thermalflow, RELACS® or DSA process. A hole pattern is shrunk by coating ashrink agent thereto, and baking such that the shrink agent may undergocrosslinking at the resist surface as a result of the acid catalystdiffusing from the resist layer during bake, and the shrink agent mayattach to the sidewall of the hole pattern. The bake is preferably at atemperature of 70 to 180° C., more preferably 80 to 170° C., for a timeof 10 to 300 seconds. The extra shrink agent is stripped and the holepattern is shrunk.

EXAMPLE

Examples of the invention are given below by way of illustration and notby way of limitation. The abbreviation “pbw” is parts by weight.

Quenchers 1 to 12 in the form of quaternary ammonium iodide, quaternaryammonium dibromoiodide, quaternary ammonium bromodiiodide or quaternaryammonium triiodide having the following structure were used in resistcompositions. Of Quenchers 1 to 12, some were purchased from TokyoChemical Industry Co., Ltd. or Sigma-Aldrich and the remaining wereprepared by neutralization reaction of an ammonium hydroxide withhydriodic acid.

Synthesis Example

Synthesis of Base Polymers (Polymers 1 to 3)

Base polymers were prepared by combining suitable monomers, effectingcopolymerization reaction thereof in tetrahydrofuran (THF) solvent,pouring the reaction solution into methanol for crystallization,repeatedly washing with hexane, isolation, and drying. The resultingpolymers, designated Polymers 1 to 3, were analyzed for composition by¹H-NMR spectroscopy, and for Mw and Mw/Mn by GPC versus polystyrenestandards using THF solvent.

Examples and Comparative Examples

Resist compositions were prepared by dissolving the polymer and selectedcomponents in a solvent in accordance with the recipe shown in Tables 1and 2, and filtering through a filter having a pore size of 0.2 μm. Thesolvent contained 100 ppm of surfactant PC-4430 (3M). The components inTables 1 and 2 are as identified below.

Polymers 1 to 3: identified aboveOrganic solvents: PGMEA (propylene glycol monomethyl ether acetate)

-   -   CyH (cyclohexanone)    -   PGME (propylene glycol monomethyl ether)        Acid generators: PAG 1 to PAG 4 of the following structural        formulae

Comparative Quenchers 1 to 5:

EB Lithography Patterning Test Examples 1-1 to 1-16 and ComparativeExamples 1-1 to 1-7

Each of the resist compositions (Tables 1 and 2) was spin coated onto asilicon substrate (which had been vapor primed withhexamethyldisilazane) and prebaked on a hotplate at 110° C. for 60seconds to form a resist film of 80 nm thick. Using a system HL-800D(Hitachi Ltd.) at an accelerating voltage of 50 kV, the resist film wasexposed imagewise to EB in a vacuum chamber. Immediately after theexposure, the resist film was baked (PEB) on a hotplate at thetemperature shown in Tables 1 and 2 for 60 seconds and developed in a2.38 wt % TMAH aqueous solution for 30 seconds to form a pattern.

The resist pattern was evaluated as follows. In the case of positiveresist film, the resolution is a minimum trench size at the exposuredose that provides a resolution as designed of a 120-nm trench pattern.In the case of negative resist film, the resolution is a minimumisolated line size at the exposure dose that provides a resolution asdesigned of a 120-nm isolated line pattern. In the case of positiveresist film, the sensitivity is the exposure dose that provides aresolution to the 120 nm trench pattern. In the case of negative resistfilm, the sensitivity is the exposure dose that provides a resolution tothe 120 nm isolated line pattern. The 120-nm isolated line pattern wasobserved under CD-SEM (S-9200, Hitachi High-Technologies Corp.) todetermine LWR. It is noted that Examples 1-1 to 1-15 and ComparativeExamples 1-1 to 1-6 are positive resist compositions, and Example 1-16and Comparative Example 1-7 are negative resist compositions.

The results are shown in Tables 1 and 2.

TABLE 1 Acid PEB Polymer generator Quencher Organic solvent temp.Sensitivity LWR Resolution (pbw) (pbw) (pbw) (pbw) (° C.) (μC/cm²) (nm)(nm) Example 1-1 Polymer 1 — Quencher 1 PGMEA (400) 80 39 3.8 75 (100)(3.70) CyH (2,000) PGME (100) 1-2 Polymer 1 — Quencher 2 PGMEA (400) 8036 3.4 75 (100) (5.29) CyH (2,000) PGME (100) 1-3 Polymer 1 — Quencher 3PGMEA (400) 80 33 3.3 75 (100) (5.76) CyH (2,000) PGME (100) 1-4 Polymer1 — Quencher 4 PGMEA (400) 80 28 3.1 75 (100) (6.23) CyH (2,000) PGME(100) 1-5 Polymer 1 — Quencher 5 PGMEA (400) 80 37 3.3 75 (100) (3.60)CyH (2,000) PGME (100) 1-6 Polymer 1 — Quencher 6 PGMEA (400) 80 32 3.675 (100) (2.82) CyH (2,000) PGME (100) 1-7 Polymer 1 — Quencher 7 PGMEA(400) 80 37 3.8 75 (100) (2.89) CyH (2,000) PGME (100) 1-8 Polymer 1 —Quencher 8 PGMEA (400) 80 39 3.6 75 (100) (3.51) CyH (2,000) PGME (100)1-9 Polymer 1 — Quencher 9 PGMEA (400) 80 38 3.7 75 (100) (3.19) CyH(2,000) PGME (100) 1-10 Polymer 1 — Quencher 10 PGMEA (400) 80 39 3.2 75(100) (5.25) CyH (2,000) PGME (100) 1-11 Polymer 1 — Quencher 11 PGMEA(400) 80 33 3.5 75 (100) (3.01) CyH (2,000) PGME (100) 1-12 Polymer 1 —Quencher 12 PGMEA (400) 80 31 3.4 75 (100) (4.15) CyH (2,000) PGME (100)1-13 Polymer 1 PAG 1 Quencher 4 PGMEA (400) 80 23 3.3 75 (100) (15)(6.23) CyH (2,000) PGME (100) 1-14 Polymer 1 PAG 3 Quencher 4 PGMEA(400) 80 18 3.1 75 (100) (18) (6.23) CyH (2,000) PGME (100) 1-15 Polymer2 PAG 2 Quencher 4 PGMEA (2,000) 90 35 4.5 80 (100) (10) (6.23) CyH(500) 1-16 Polymer 3 PAG 4 Quencher 4 PGMEA (2,000) 100 39 4.9 80 (100)(10) (6.23) CyH (500)

TABLE 2 Acid PEB Polymer generator Quencher Organic solvent temp.Sensitivity LWR Resolution (pbw) (pbw) (pbw) (pbw) (° C.) (μC/cm²) (nm)(nm) Comparative 1-1 Polymer 1 — Comparative PGMEA (400) 80 59 5.8 85Example (100) Quencher 1 CyH (2,000) (2.50) PGME (100) 1-2 Polymer 1 —Comparative PGMEA (400) 80 57 5.7 85 (100) Quencher 2 CyH (2,000) (4.42)PGME (100) 1-3 Polymer 1 — Comparative PGMEA (400) 80 56 4.3 80 (100)Quencher 3 CyH (2,000) (3.63) PGME (100) 1-4 Polymer 1 — ComparativePGMEA (400) 80 57 4.6 80 (100) Quencher 4 CyH (2,000) (3.23) PGME (100)1-5 Polymer 1 — Comparative PGMEA (400) 80 61 5.5 80 (100) Quencher 5CyH (2,000) (3.20) PGME (100) 1-6 Polymer 2 PAG 2 Comparative PGMEA(2,000) 90 44 7.6 85 (100) (10) Quencher 1 CyH (500) (2.50) 1-7 Polymer3 PAG 1 Comparative PGMEA (2,000) 100 60 8.4 90 (100) (10) Quencher 1CyH (500) (2.50)

EUV Lithography Test Examples 2-1 to 2-12 and Comparative Example 2-1

The resist composition in Table 3 was spin coated on a silicon substratehaving a 20 nm coating of silicon-containing spin-on hard mask SHB-A940(Shin-Etsu Chemical Co., Ltd., silicon content 43 wt %) and prebaked ona hotplate at 105° C. for 60 seconds to form a resist film of 60 nmthick. Using an EUV scanner NXE3300 (ASML, NA 0.33, σ0.9/0.6, quadrupoleillumination), the resist film was exposed to EUV through a mask bearinga hole pattern at a pitch 46 nm (on-wafer size) and +20% bias. Theresist film to was baked (PEB) on a hotplate at the temperature shown inTable 3 for 60 seconds and developed in a 2.38 wt % TMAH aqueoussolution for 30 seconds to form a hole pattern having a size of 23 nm.

The resist pattern was evaluated using CD-SEM (CG-5000, HitachiHigh-Technologies Corp.). The exposure dose that provides a hole patternhaving a size of 23 nm is reported as sensitivity. The size of 50 holeswas measured, from which a size variation (3σ) was computed and reportedas CDU.

The resist composition is shown in Table 3 together with the sensitivityand CDU of EUV lithography.

TABLE 3 Acid PEB Polymer generator Quencher Organic solvent temp.Sensitivity CDU (pbw) (pbw) (pbw) (pbw) (° C.) (mJ/cm²) (nm) Example 2-1Polymer 1 — Quencher 1 PGMEA (400) 80 24 3.3 (100) (3.70) CyH (2,000)PGME (100) 2-2 Polymer 1 — Quencher 2 PGMEA (400) 80 25 3.0 (100) (5.29)CyH (2,000) PGME (100) 2-3 Polymer 1 — Quencher 3 PGMEA (400) 80 25 2.9(100) (5.76) CyH (2,000) PGME (100) 2-4 Polymer 1 — Quencher 4 PGMEA(400) 80 21 3.1 (100) (6.23) CyH (2,000) PGME (100) 2-5 Polymer 1 —Quencher 5 PGMEA (400) 80 24 2.6 (100) (3.60) CyH (2,000) PGME (100) 2-6Polymer 1 — Quencher 6 PGMEA (400) 80 28 2.6 (100) (2.82) CyH (2,000)PGME (100) 2-7 Polymer 1 — Quencher 7 PGMEA (400) 80 25 2.8 (100) (2.89)CyH (2,000) PGME (100) 2-8 Polymer 1 — Quencher 8 PGMEA (400) 80 28 2.8(100) (3.51) CyH (2,000) PGME (100) 2-9 Polymer 1 — Quencher 9 PGMEA(400) 80 26 2.9 (100) (3.19) CyH (2,000) PGME (100) 2-10 Polymer 1 —Quencher 10 PGMEA (400) 80 26 2.9 (100) (5.25) CyH (2,000) PGME (100)2-11 Polymer 1 Quencher 11 PGMEA (400) 80 26 2.9 (100) (3.01) CyH(2,000) PGME (100) 2-12 Polymer 1 PAG 3 Quencher 8 PGMEA (400) 80 23 2.9(100) (10) (5.20) CyH (2,000) PGME (100) Comparative 2-1 Polymer 1 —Comparative PGMEA (400) 80 38 3.5 Example (100) Quencher 1 CyH (2,000)(2.50) PGME (100)

It is demonstrated in Tables 1 to 3 that resist compositions comprisinga quaternary ammonium iodide, quaternary ammonium dibromoiodide,quaternary ammonium bromodiiodide of quaternary ammonium triiodide formpatterns having a high sensitivity, satisfactory resolution, and reducedLWR or CDU.

Japanese Patent Application No. 2016-224748 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A chemically amplified resist composition comprising a quenchercontaining a quaternary ammonium salt selected from the group consistingof a quaternary ammonium iodide, quaternary ammonium dibromoiodide,quaternary ammonium bromodiiodide, and quaternary ammonium triiodide,and an acid generator.
 2. The resist composition of claim 1 wherein thequaternary ammonium salt has the formula (1) or (2):

wherein R¹ to R⁴ and R⁵ to R¹⁰ are each independently a C₁-C₂₄ straight,branched or cyclic alkyl group, C₂-C₂₄ straight, branched or cyclicalkenyl group, C₂-C₂₄ straight, branched or cyclic alkynyl group, orC₆-C₂₄ aryl group, which may contain a halogen, hydroxyl, carboxyl,ether, ester, thiol, thioester, thionoester, dithioester, amino, nitro,sulfone or ferrocenyl moiety, a pair of R¹ and R², R¹ and R⁴, R² and R³,and/or R³ and R⁴ may bond together to form a ring, or a pair of R¹ andR², R¹ and R⁴, R² and R³, or R³ and R⁴, taken together, may form adouble bond, R¹¹ is a C₂-C₁₂ straight, branched or cyclic alkylene groupwhich may contain an ether and/or ester moiety, X⁻ is an anion selectedfrom the group consisting of I⁻, Br₂I⁻, BrI₂ ⁻ and I₃ ⁻.
 3. The resistcomposition of claim 1 wherein the acid generator is capable ofgenerating sulfonic acid, imidic acid or methide acid.
 4. The resistcomposition of claim 1, further comprising a base polymer.
 5. The resistcomposition of claim 4 wherein the base polymer comprises recurringunits of at least one type selected from recurring units having theformulae (f1) to (f3):

wherein R^(A) is each independently hydrogen or methyl, Z¹ is a singlebond, phenylene, —O—Z¹¹—, or —C(═O)—Z¹²—Z¹¹—, Z¹¹ is a C₁-C₆ straight,branched or cyclic alkylene group or C₂-C₆ straight, branched or cyclicalkenylene group which may contain a carbonyl, ester, ether or hydroxylmoiety, or phenylene group, Z¹² is —O— or —NH—, R⁵¹, R⁵², R⁵³, R⁵⁴, R⁵⁵,R⁵⁶, R⁵⁷, and R⁵⁸ are each independently a C₁-C₁₂ straight, branched orcyclic alkyl group which may contain a carbonyl, ester or ether moiety,or a C₆-C₁₂ aryl, C₇-C₂₀ aralkyl, or mercaptophenyl group, Z² is asingle bond, —Z²¹—C(═O)—O—, —Z²¹—O—, or —Z²¹—O—C(═O)—, Z²¹ is a C₁-C₁₂straight, branched or cyclic alkylene group which may contain acarbonyl, ester or ether moiety, Z³ is a single bond, methylene,ethylene, phenylene, fluorinated phenylene, —O—Z³¹—, or —C(═O)—Z³²—Z³¹—,Z³¹ is a C₁-C₆ straight, branched or cyclic alkylene group or C₂-C₆straight, branched or cyclic alkenylene group which may contain acarbonyl, ester, ether or hydroxyl moiety, or a phenylene, fluorinatedphenylene or trifluoromethyl-substituted phenylene group, Z³² is —O— or—NH—, A¹ is hydrogen or trifluoromethyl, and M⁻ is a non-nucleophiliccounter ion.
 6. The resist composition of claim 1 wherein the acidgenerator also functions as a base polymer.
 7. The resist composition ofclaim 6 wherein the acid generator is a polymer comprising recurringunits of at least one type selected from recurring units having theformulae (f1) to (f3):

wherein R^(A) is each independently hydrogen or methyl, Z¹ is a singlebond, phenylene, —O—Z¹¹—, or —C(═O)—Z¹²—Z¹¹—, Z¹¹ is a C₁-C₆ straight,branched or cyclic alkylene group or C₂-C₆ straight, branched or cyclicalkenylene group which may contain a carbonyl, ester, ether or hydroxylmoiety, or phenylene group, Z¹² is —O— or —NH—, R⁵¹, R⁵², R⁵³, R⁵⁴, R⁵⁵,R⁵⁶, R⁵⁷, and R⁵⁸ are each independently a C₁-C₁₂ straight, branched orcyclic alkyl group which may contain a carbonyl, ester or ether moiety,or a C₆-C₁₂ aryl, C₇-C₂₀ aralkyl, or mercaptophenyl group, Z² is asingle bond, —Z²¹—C(═O)—O—, —Z²¹—O—, or —Z²¹—O—C(═O)—, Z²¹ is a C₁-C₁₂straight, branched or cyclic alkylene group which may contain acarbonyl, ester or ether moiety, Z³ is a single bond, methylene,ethylene, phenylene, fluorinated phenylene, —O—Z³¹—, or —C(═O)—Z³²—Z³¹—,Z³¹ is a C₁-C₆ straight, branched or cyclic alkylene group or C₂-C₆straight, branched or cyclic alkenylene group which may contain acarbonyl, ester, ether or hydroxyl moiety, or a phenylene, fluorinatedphenylene or trifluoromethyl-substituted phenylene group, Z³² is —O— or—NH—, A¹ is hydrogen or trifluoromethyl, and M⁻ is a non-nucleophiliccounter ion.
 8. The resist composition of claim 4 wherein the basepolymer comprises recurring units having the formula (a1) or recurringunits having the formula (a2):

wherein R^(A) is each independently hydrogen or methyl, R¹¹ and R¹² areeach independently an acid labile group, X¹ is a single bond, phenylene,naphthylene, or a C₁-C₁₂ linking group containing ester moiety orlactone ring, and X² is a single bond or ester group.
 9. The resistcomposition of claim 8 which is a chemically amplified positive resistcomposition.
 10. The resist composition of claim 4 wherein the basepolymer is an acid labile group-free polymer.
 11. The resist compositionof claim 10 which is a chemically amplified negative resist composition.12. The resist composition of claim 1, further comprising an organicsolvent.
 13. The resist composition of claim 1, further comprising asurfactant.
 14. A pattern forming process comprising the steps ofcoating the resist composition of claim 1 onto a substrate, baking,exposing the resulting resist film to high-energy radiation, anddeveloping the resist film with a developer.
 15. The process of claim 14wherein the high-energy radiation is ArF excimer laser of wavelength 193nm or KrF excimer laser of wavelength 248 nm.
 16. The process of claim14 wherein the high-energy radiation is EB or EUV of wavelength 3 to 15nm.